Oil-based lubricants (e.g., mineral oils) commonly include additives for reducing friction between, and wear of, iron-based parts (e.g., steel, cast iron, etc.). Such additives slowly chemically react with the metal surfaces to form an iron phosphate film thereon which provides the lower friction and wear characteristics. Wang et al U.S. Pat. No. 4,714,529, discloses and claims anodizing iron-based parts in an electrolytic medium comprising an oil-based lubricant and a dialkyl hydrogen phosphate, such as dilauryl hydrogen phosphate or mixed-dialkyl acid orthophosphate, (hereafter DHP) to more rapidly electrochemically form thicker more uniform iron phosphate films. Wang et al is intended to be incorporated herein by reference. According to Wang et al, the anodic iron-based workpiece is closely spaced (i.e., ca. 0.15 mm) from a cathodic counterelectrode in the DHP-medium and current passed therebetween to electrochemically form the desired iron phosphate film. In Wang et al, it is believed that: the DHP dissociates in the lubricant to form hydrogen cations and a corresponding organic anion; as current passes, iron dissolves from the workpiece surface (i.e., as ferrous ions) and immediately reacts with the organic anions to form the amorphous iron phosphate coating [i.e., Fe.sub.3 (PO.sub.4).sub.2 ]; and the hydrogen ions migrate to the cathode and form H.sub.2 thereat.
While the Wang et al process is effective to produce friction and wear reducing iron phosphate films, the inherently high electrical resistivity (i.e., ca.&gt;10.sup.9 ohm-cm) of the DHP-oil medium limits use of the process to electrodes which are separated by no more than about 200 micrometers at all locations thereof and hence requires conforming electrodes. Such a restriction limits the practical application of the Wang et al process particularly with respect to the application thereof to forming films on complex-shaped surfaces (e.g., camshaft lobes) having some portions thereof proximate (i.e., within about 200 .mu.m) and other portions more remote (i.e., significantly greater than 200 .mu.m) from the cathode.
It is an object of the present invention to so increase the electrical conductance of a dialkyl hydrogen phosphate anodizing medium as to substantially improve its ability to form amorphous iron phosphate friction and wear reducing films on complex iron workpiece surfaces which have some portions proximate the cathode and other portions remote therefrom and thereby extend the usefulness of the process without the need for conforming electrodes. This and other objects and advantages of the present invention will be more readily apparent from the detailed description thereof which is given hereafter.